FIG. 10 shows typical conventional cement manufacturing facilities.
The cement manufacturing facilities generally include a rotary kiln 1 adapted to burn cement materials, a preheater 4 equipped with plural cyclones installed in a kiln inlet part 2 of the rotary kiln 1, a chute 5 adapted to supply the cement materials from a cyclone in the last stage of the preheater 4 to the kiln inlet part 2 of the rotary kiln 1, an exhaust line 6 connected to a cyclone in the first stage and adapted to discharge combustion exhaust gas, and a main burner 7 installed in a kiln outlet part 3 and adapted to heat an inner part of the rotary kiln 1.
In the manufacturing facilities for cement clinker described above, the cement materials supplied to the preheater 4 drop to lower cyclones in sequence and get preheated by undergoing heat exchange with high-temperature exhaust gas rising upward from the rotary kiln 1. Then, the cement materials are introduced into the kiln inlet part 2 of the rotary kiln 1 through the chute 5 in the last stage and burned in the process of being sent through the rotary kiln 1 from the side of the kiln inlet part 2 to the kiln outlet part 3 to become cement clinker.
In such cement manufacturing facilities, chlorine compound contained in the cement materials or chlorine compound induced in waste such as plastics inputted as part of fuel volatilizes mainly as alkali chloride such as KCl or NaCl in a high-temperature (approximately 1,400° C.) atmosphere in the rotary kiln 1 and moves into exhaust gas. The exhaust gas is discharged from the kiln inlet part 2 of the rotary kiln 1 to the side of the preheater 4. Then, when rising from lower cyclones to upper cyclones in sequence, the exhaust gas is cooled by preheating the cement materials, and chlorine compound contained in the exhaust gas moves into the side of the cement materials again.
Consequently, since the chlorine content circulates in a system made up of the rotary kiln 1 and the preheater 4, chlorine compound and the like newly carried into the system by the fuel or cement raw materials cause gradual increase in chlorine concentration in the system, eventually blocking the cyclones of the preheater 4 and thereby obstructing the operation. Thus, in recent years, a chlorine bypass device has come to be installed in the cement manufacturing facilities to remove the chlorine compound in the system.
The chlorine bypass device includes an extraction pipe 9 connected to an exhaust gas pipe 8 coming from the kiln inlet part 2 and adapted to extract part of exhaust gas, a cooling pipe 10 adapted to mix the exhaust gas extracted by the extraction pipe 9 with cooling air supplied from a blower 10a and thereby cool the exhaust gas, a cyclone 11 adapted to separate and remove cement materials from the exhaust gas in the extraction pipe 9, and a bag filter (collector) 12 adapted to collect chloride dust contained in the exhaust gas which has passed through the cyclone 11.
The chlorine bypass device described above can periodically or continuously bleed part of the exhaust gas using the extraction pipe 9 when the exhaust gas is discharged from the rotary kiln 1 via the exhaust gas pipe 8, cool the exhaust gas using the cooling pipe 10, thereby condense chloride gas contained in the exhaust gas and separate out chloride dust, then selectively remove dust of cement raw materials with large particle sizes from the exhaust gas using the cyclone 11, subsequently recover chloride dust having small particle sizes from the accompanying exhaust gas using the bag filter 12 in a succeeding stage, and thereby prevent rises in the chlorine concentration in the system.
In the chlorine bypass device of the above configuration, the cooling pipe 10 adapted to mix the exhaust gas extracted by the extraction pipe 9 with cooling air, is intended to cool the exhaust gas temperature to such a level that the exhaust gas can be supplied to the bag filter 12 in a succeeding stage as well as to condense the chloride gas contained in the exhaust gas into chloride dust.
Conventionally, a double wall pipe structure such as shown in FIG. 11 is generally used for such a cooling pipe 10.
The cooling pipe 10 includes an outer pipe 13 connected at one end to the exhaust gas pipe 8 and closed at another end, and a supply pipe 14 connected to the closed end of the outer pipe 13 in a direction orthogonal to the outer pipe 13 and adapted to supply cooling air sent from the blower 10a, wherein the extraction pipe 9 is inserted coaxially into the outer pipe 13 through the closed end of the outer pipe 13.
The cooling pipe 10 is designed such that part of the exhaust gas flowing into the outer pipe 13 from the exhaust gas pipe 8 will be cooled by being mixed with the cooling air in the outer pipe 13 and sent from the extraction pipe 9 to the cyclone 11, where the cooling air is flowing down between the outer pipe 13 and the extraction pipe 9 by being supplied from the supply pipe 14. Incidentally, cooling means found in Patent Literatures 1 to 3 described below generally have a configuration similar to the one described above.